ADF&G Home » Species » Animals » Steelhead and Rainbow Trout

Jump to species:

Printer friendly

Description Uses Management Research Get Involved More Resources

Did You Know?

Nearly all of the rainbow and

steelhead trout caught and

released by anglers will survive if

handled properly.

Description Life History Range and Habitat Status, Trends, and Threats Fast Facts

General Description

Rainbow and steelhead trout are the most widely known trout in the world and are highly sought

after by anglers because of their strong fighting abilities. In Alaska, there are two commonly

recognized forms of the rainbow trout and these sub-groupings or “forms” are based primarily on

where they spend their time feeding and maturing. The most common rainbow trout in Alaska is

the stream-resident form that lives its life entirely in freshwater with maybe short periods of time

spent in estuarine or near-shore marine waters. The second form is commonly known as

steelhead and these rainbow trout leave freshwater as juveniles and migrate long distances in the

ocean where they grow to maturity before migrating back to their original home waters.

Since rainbow and steelhead trout are the same species there are no major physical differences

between them, however, the nature of their differing lifestyles has resulted in subtle differences in

color, shape, size, and general appearance. Juvenile steelhead are indistinguishable from

(Oncorhynchus mykiss)

Photo Gallery Video

View Large Map

Steelhead / Rainbow Trout Species Profile, Alaska Department of Fish a... http://www.adfg.alaska.gov/index.cfm?adfg=steelhead.main

1 of 2 4/20/2016 4:17 PM
juvenile rainbow trout during the first few years of their life. Young trout have eight to thirteen parr

marks on their sides and five to ten parr marks between the top of the head and dorsal fin. The

adipose fin usually has a continuous outline of black surrounded by a clear window and the lower

jaw (maxillary) typically does not extend past the back margin of the eye. Prior to their seaward

migration juvenile steelhead go through a series of physical changes called smoltification which

allows them to survive in saltwater; during this process the fish lose their parr marks and become

silvery in color.

Within a year or so of hatching the stream resident form of rainbow trout possess the well-known

streamlined salmonid form, though body shape and coloration vary widely and reflect habitat,

age, sex, and degree of maturity. The body shape may range from slender to thick. The back may

shade from blue-green to olive. There is a reddish-pink band along each side about the midline

that may range from faint to radiant. The lower sides are usually silver, fading to pure white

beneath. Small black spots are present over the back above the lateral line, as well as on the

upper fins and tail. In some locations, the black spots of adults may extend well below the lateral

line and even cover the entire lower side. Rainbow trout are positively identified by the 8 to 12

rays in the anal fin, a mouth that does not extend past the back of the eye, and the lack of teeth at

the base of the tongue. River or stream residents normally display the most intense pink stripe

coloration and heaviest spotting followed by rainbows from lake and lake-stream systems.

Spawning trout are characterized by generally darker coloration.

Adult steelhead which have spent 1 to 3 years in the ocean are generally heavily spotted with

irregularly shaped dark spots both above and below the lateral line. Small spots are also

scattered along the top of the head, along the sides, on the dorsal and both lobes of the caudal

fins. Steelhead are typically silvery or brassy in color but may range from steely blue and emerald

green to olive. Steelhead fresh from the ocean can be very bright and much more silver in color

than resident rainbow. The classic band of color along the lateral line, which rainbow trout are

named for, can range from light pink to deep red with mature males having the brightest colors.

Although typically larger in size, steelhead are generally more slender and streamlined than

stream resident rainbow trout. On steelhead the typical colors and spots of the trout appear to be

coming from beneath a dominant silvery sheen which gradually fades in fresh water and

steelhead become difficult to differentiate from mature resident rainbow trout. The distinct and

beautiful coloration of steelhead during the freshwater spawning period is important for mating

and reproduction while the silvery sheen and streamlined shape of ocean-bright steelhead is

essential to survival in the ocean environment.

Stream resident rainbow trout and juvenile steelhead can usually be distinguished from their close

relative the cutthroat trout because rainbow trout do not have the classic red or “cutthroat” slash

on the underside of their lower jaw. However not all cutthroat trout have this slash and there are

naturally occurring rainbow/cutthroat trout hybrids which have physical markings of both.

Biologists often use the presence/absence of small teeth at the base of the tongue called

basibranchial teeth as a means to distinguish between steelhead (teeth absent) and cutthroat

trout (teeth present).

Steelhead / Rainbow Trout Species Profile, Alaska Department of Fish a... http://www.adfg.alaska.gov/index.cfm?adfg=steelhead.main

2 of 2 4/20/2016 4:17 PM